The invention is related to audio and video data recording and reproduction and, in particular, an apparatus and method for controlling a tape transport based on a previously recorded control signal, which is reproduced from a longitudinal track or, alternatively, based on a previously recorded track number, which is reproduced from a slant track.
To eliminate guard-bands thereby achieving more recording area on a tape in a video tape recorder (VTR), the azimuth angles are alternated for the adjacent slant tracks on which audio and video data is recorded. If, due to crosstalk or misalignment, a slant track is erroneously scanned or traced by a helical-type playback head employing a different azimuth angle, the audio and video data on that track is not reproduced, as it should not be.
This no-guard band arrangement, however, requires tight tracking control for maintaining accurate data reproduction. If the playback head and the slant track of the same azimuth angle deviate from each other, many errors may occur during the reproduction of audio and video data.
One type of the tracking control has been proposed in a VTR using a so-called non-tracking system. The VTR with the non-tracking system has two playback heads, each having a positive azimuth angle (hereinafter referred to as positive azimuth heads) and spaced apart by one track pitch along the width of a tape surface. Further, the VTR has two additional playback heads. Each of these additional playback heads has a negative azimuth angle (hereinafter referred to as negative azimuth heads) and is also arranged at an interval of one track pitch. The negative azimuth heads may be symmetrically positioned, with respect to the center of a drum, across from the positive azimuth heads.
In the VTR equipped with such non-tracking system, the slant tracks are scanned by the four playback heads for reading the audio and video data. Initially, the received audio and video data is processed in order to detect and correct errors using an inner parity code. Next, a priority is given to the data with no errors, after the error correction processing, as opposed to the audio and video data in which errors cannot be corrected. The error-corrected data is then stored in a VTR memory. Further, the audio and video data is error-corrected using an outer parity code. Similarly, the audio and video data having the least number of errors is output. Hence, by selecting the best audio and video data between the two positive (and negative) azimuth heads, requirements for accurately controlling the tracking of a slant track by the playback heads are greatly relaxed. It then becomes possible to record audio and video data without scanning a helical track already existing on the tape (a so-called underlying track).
In addition, a track is typically provided along the longitudinal direction of the tape. In another type of tracking control in a general VTR, when the audio and video data is recorded on the slant tracks of the tape, the control signal is simultaneously recorded on the control track by a separate control head. When the audio and video data is reproduced from the slant tracks, the control signal is also reproduced from the control track by the control head. Accurate data reproduction from the tape is thereby achieved as a function of the tracking control, due to the reproduced control signal, by either accelerating or decelerating the tape transport.
However, when the control head performing the recording and reproduction of the control signal from the longitudinal track of the tape becomes unusable due to clogging (i.e., head clogging), for example, the tape transport cannot be controlled. Consequently, data is either reproduced incorrectly or not reproduced at all.
Furthermore, a particular position at which the control signal is recorded may not coincide with the corresponding recording position of the audio and video data due to various causes, such as an error in the tape transport system, the stretching or shrinkage of the tape, etc. In such a case, if transporting of the tape is based on the control signal, for example, when the audio and video data compressed and coded in units of GOP (group of pictures) is reproduced by the MPEG (Motion Picture Experts Group) system, it is possible that the audio and video data near the GOP boundaries can no longer be correctly reproduced.
Even in a VTR employing the non-tracking system as described above, the scanning direction of the reproducing head may diverge from the direction of the slant track itself due to lack of control of the tape transport as used in a general VTR. When this occurs, the audio and video data will no longer be properly reproduced by the VTR with the non-tracking system.
A need therefore exists for an apparatus and method that overcome the above disadvantages.